Conventional refrigeration systems including refrigerant circuits performing refrigeration cycles by circulating refrigerants are known. Examples of such refrigeration systems include a so-called multi-type refrigeration system in which a plurality of indoor units are connected in parallel to one outdoor unit (see, for example, Patent Document 1).
In this refrigeration system, the outdoor unit includes an outdoor circuit, and the indoor units include indoor circuits. The outdoor circuit includes a compressor, an outdoor heat exchanger, an outdoor expansion valve, and a receiver, for example. Each of the indoor circuits includes an indoor heat exchanger and an indoor expansion valve. A refrigerant circuit of the refrigeration system is configured by connecting the indoor circuits in parallel to the outdoor circuit.
Example of methods for adjusting the amount of heat exchange in the indoor units of the refrigeration system include a method of performing capacity control of the compressor and refrigerant outlet superheat degree control with the indoor expansion valves. The capacity control of the compressor is performed based on a pressure detected by a refrigerant-pressure sensor provided at the suction side of the compressor. Specifically, the operating frequency of the compressor is adjusted such that a saturation temperature (i.e., an evaporation temperature) corresponding to the pressure calculated from the detected pressure approaches a predetermined evaporation temperature (hereinafter referred to as a set temperature).
With this configuration, when the current evaporation temperature is lower than the set temperature in the capacity control of the compressor, the operating frequency of the compressor is reduced to reduce the capacity of the compressor. Then, power consumption of the compressor decreases, and the evaporation temperature increases, resulting in that the evaporation temperature approaches the set temperature. On the other hand, when the current evaporation temperature is higher than the set temperature, the operating frequency of the compressor is increased to increase the capacity of the compressor. Then, power consumption of the compressor increases, and the evaporation temperature decreases, resulting in that the evaporation temperature approaches the set temperature.
The refrigerant outlet superheat degree control is performed based on a temperature detected by a refrigerant outlet temperature sensor provided at the outlet of each of the indoor heat exchangers and a pressure detected by the refrigerant-pressure sensor. Specifically, the opening degree of each of the indoor expansion valves of the indoor heat exchangers is adjusted such that the refrigerant outlet superheat degree for each of the indoor units calculated from the detected temperature and the detected pressure reaches a target superheat degree determined according to the amount of heat exchange necessary for the indoor heat exchanger of the indoor unit. In this operation, the amount of heat exchange necessary for the indoor heat exchanger is determined based on a deviation between an indoor set temperature and an indoor temperature of a room in which the indoor heat exchanger is located.
With this configuration, when the indoor temperature is higher than the indoor set temperature in the refrigerant outlet superheat degree control, the target superheat degree is set at a degree lower than the current degree. Then, a deviation occurs between the current refrigerant outlet superheat degree and the target superheat degree, and the opening degree of the indoor expansion valve increase so as to increase the deviation. On the other hand, when the indoor temperature is lower than the indoor set temperature, the target superheat degree is set at a degree higher than the current degree. Then, a deviation occurs between the current refrigerant outlet superheat degree and the target superheat degree, and the opening degree of the indoor expansion valve decrease so as to reduce the deviation. In this manner, the opening degrees of the indoor expansion valves are adjusted to adjust the flow rate of refrigerants flowing in the indoor heat exchangers, thereby increasing or decreasing the amount of heat exchange in the indoor heat exchangers so that the indoor temperature approaches the indoor set temperature of the room.